The present invention relates generally to a welding-type system and, more particularly, to a system and method for controlling the harmonics injected onto an input power line during the operation of a welding-type system.
Welding-type systems, such as welders, plasma cutters, and induction heaters, often include an inverter-based power source that is designed to condition high power to carrying out a desired process. These inverter-based power sources, often referred to as switched-mode power supplies, can take many forms. For example, they may include a half-bridge inverter topology, a full-bridge inverter topology, a forward-converter topology, a flyback topology, a boost-converter topology, a buck-converter topology, and combinations thereof.
Regardless of the specific inverter topology employed, referring to FIG. 1, an inverter-based power source systems 10 typically includes a variety of components, such as an input filter 12, first rectifier 14, an inverter 16, an analog controller 18, and a second rectifier 20 that is connected to an output 22. While FIG. 1 is a simplified overview of common components of an inverter-based power source system 10, it is contemplated that additional components may be included, such as filtering components, feedback and control loops, and transformers or other converters designed to provide a desired output power characteristic.
During operation, the system 10 is connected to a supply of power 24 that provides alternating-current (AC) power, for example, as received from a utility grid over transmission power lines 26. The rectifier 12 is designed to receive the AC power from the supply of power 24 and convert the AC power to DC power that is delivered to a DC bus 28. Specifically, the rectifier 20 includes a plurality of switches that rectify the AC power received from the supply of power 24.
The DC power is delivered from the rectifier 12 over the DC bus 28 to the inverter 16. The inverter 16 includes a plurality of switching devices (e.g., IGBTs or other semiconductor switches) that are positioned between the positive and negative buses 28. The inverter 16 is controlled by the analog controller 18 to open and close specific combinations of the switches to sequentially generate pulses that are delivered to the second rectifier 20 and, ultimately, to the output 22 with the desired voltage and current characteristics. Specifically, the above-described inverter-based power source system 10 is specifically designed for delivering high-power to the output 22 to drive a process such as welding, plasma cutting, and induction heating.
As described, inverter-based power sources include at least one active switching device, the inverter 16. The switching characteristics of the inverter 16 are controlled by the analog controller 18 to, along with the second rectifier 20, produce the desired output power having the desired voltage and current characteristics.
Specifically, referring now to FIG. 2, the components of a half-bridge inverter and associated analog controller are shown. However, as addressed above, it is contemplated that additional topologies, such as a full-bridge inverter topology, a forward-converter topology, a flyback topology, a boost-converter topology, a buck-converter topology, and combinations thereof, may be employed. Furthermore, it is contemplated that additional components, such as transformers and various power conditioning components, are typically employed but have not been shown in order to simply the illustrated inverter configuration.
The analog controller 18 typically includes a waveform generator 30 and a comparator 32. The waveform generator 30 generates a carrier signal or waveform having a first frequency and a first period that is passed to the comparator 32 to be compared to a sinusoidal command or modulating voltage waveform having a second, typically lower, frequency and a second, typically longer, period. Responsive thereto, the comparator 32 generates a first trigger signal and a second trigger signal corresponding to a comparison and identification of intersections of the command waveform and carrier waveform. The first trigger signal is provided to a first or “upper” switch 34 of the inverter 16 and the second trigger signal is provided to a second or “lower” switch 36 of the inverter 16. In this regard, the switches 34, 36 of the inverter 16 are caused to open and close in alternating fashion to generate a high-frequency AC signal that is provided to the rectifier 20 to produce the desired output power.
Therefore, the comparator 32 generally functions by comparing a time varying analog signal to a ramp type signal, to generate timing pulses to the switches 34, 36 of fixed frequency but with variable pulse width or “ON” time. In this regard, the comparator 32 controls the pulse width modulation (PWM) or the ON/OFF ratio of the switches 34, 36 to effectively control the output voltage and/or current as required by a feedback control loop and a commanded output level.
Unfortunately, the operation of active switching devices, such as the inverter 16, can inject high-frequency harmonics onto the power lines 26. These injected harmonics can adversely affect operation of other systems connected to the supply of power 24. Additionally, the rectifiers 14, 20 may be actively controlled as well and may, likewise, inject harmonics onto the power lines 26.
As a result, one or more filters 12 are often arranged between the supply of power 24 and the inverter-based power source 10. For example, the filter 12 may include passive filter components designed to suppress the harmonics injected onto the power lines 26 by operation of the inverter-based power source 10.
However, as power regulations become more and more stringent, the amount of high-frequency harmonics tolerated under the regulations decrease. Furthermore, since these regulations vary between countries, the amount and concentration of harmonics tolerated under such regulations varies by country.
Therefore, it would be desirable to have a system and method for accurately controlling the harmonics injected onto power supply lines during the operation of welding-type systems.